Perhaps you are thinking of Uluru or Ayers Rock in Central Australia. It is a fantastic rock formation and is famous for its changing color. It is the largest known single rock on earth and is comprised of sandstone. The color changes spectactularly with the movement of the sun throughout the day, turning a deeper and deeper red as the sun sets. The color show is repeated as the sun rises. The sandstone is infused with minerals like feldspar that make it appear to glow at sunset and sunrise. The rock gets its rust color from oxidation. It is in an area of little rain but when it does rain the rock acquires a silvery gray color with streaks of black algae in the areas that channel water. For some great photos see the link provided below.
You might be referring to Ayers Rock which appears to change colour as the sun sets.
Rock mountain.. It changes its colour daily
Metamorphic rock
The hill that changes its color is called Rainbow Mountain or Vinicunca. It is located in the Andes mountains of Peru and gets its vibrant colors from different mineral deposits in the soil.
obsidian
Uluru or Ayers Rock does not actually change colour, when it is seen in different light it appears to do so. On the few occasions it rains it turns a grey colour with streaks of black. So in this way many rocks change colour
The process by which the shape of a rock changes in response to stress is called deformation. This can result in folding, faulting, or fracturing of the rock.
Under a big rock or in the shade
False Sedimetary rocks can be formed from changes in igneous rock, and igneous rock can be from changes in sedimentary rock.
the rock cycle
The colour of Uluru/Ayers Rock, at close range, is an orange-red ochre colour. In the normal light of day, from a distance, it takes on a browner hue. Its different colours are quite remarkable. At sunrise, it has a more orange-yellow appearance. During tain, it has a silver-grey appearance. There are several factors which contribute to the appearance of different colour changes for Uluru at different times of day. The different angles of morning sun and late afternoon sun reflect differently off the surface of the Rock, and interact with the different soil colours surrounding the Rock, to also alter its appearance from the brilliant orange-red of early morning to the deeper, dusky-red of later afternoon. On an overcast day, the Rock's colour is also more subdued, turning to an orange-brown colour. It is largely a matter of the atmospheric conditions, and how the moisture levels in the air and any clouds reflect the surrounding desert colours back onto Uluru.
When you have a volcano the molten rock is called Magma when it is inside the volcano but when it gets out of the volcano it changes name to Lava.